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Water Resources and Industry

Water Resources and Industry 4 (2013) 51–67

2212-37http://d

n CorrE-m

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Adsorption studies of arsenic(III) removal fromwater by zirconium polyacrylamide hybridmaterial (ZrPACM-43)

Sandip Mandal, Manoj Kumar Sahu, Raj Kishore Patel n

Department of Chemistry, National Institute of Technology, Rourkela, Odisha, 769008, India

a r t i c l e i n f o

Article history:Received 17 May 2013Received in revised form10 September 2013Accepted 12 September 2013

Keywords:AdsorptionAASArsenicXRDZirconium

17 & 2013 The Authors. Published by Elsevx.doi.org/10.1016/j.wri.2013.09.003

esponding author. Tel.: þ91 0661 246 265ail addresses: sandipmandal9@gmail.com (

a b s t r a c t

A novel hybrid material zirconium polyacrylamide (ZrPACM-43) wassynthesized by mixing aqueous solution of zirconium oxychloride andmixture of acrylamide following an environmental friendly sol–gelmethod. The material was characterized by FTIR, XRD, TGA-DTA, andSEM-EDS. The extent of arsenic removal capacity was tested by thematerial by varying the solution parameters like adsorbent dose,adsorbate concentration, pH of the solution, contact time andtemperature. The maximum removal efficiency of arsenic(III) was98.22% under optimum conditions with adsorption equilibrium timeof 120 min. The adsorption process followed second order kineticsand adsorption data were best fitted to linearly transformedFreundlich isotherm with correlation coefficient of R240.999.Adsorption capacity (qo) calculated from Langmuir isotherm wasfound to be 41.48mg g�1. The thermodynamic parameter ΔHindicates an endothermic adsorption process. The regeneration studyshows that the material is regenerated by 1 M alkali solution.

& 2013 The Authors. Published by Elsevier B.V.

Open access under CC BY-NC-ND license.

1. Introduction

The use of heavy metals and their compounds has increased the comfort of human being in great way.They are used in different processes [1]. The excessive use of heavymetals andmetalloids causes to increase

ier B.V.

2, þ91 9437245438, þ91 9778212090; fax: þ91 661 246 2651.S. Mandal), rkpatel@nitrkl.ac.in, rkpatelnitr@gmail.com (R.K. Patel).

Open access under CC BY-NC-ND license.

S. Mandal et al. / Water Resources and Industry 4 (2013) 51–6752

their concentration in aquatic systems. Arsenic is a metalloid, a known poison element, and exists as oxideor anion and known to be 20th most abundant element in the earth [1]. The presence of arsenic in water isdue to natural weathering process, geochemical reactions, biological activity, combustion of fossil fuels,volcanic eruptions, gold mining, leaching of man-made arsenic compounds, smelting of metals ores,desiccants, wood preservatives, agricultural pesticides and many other anthropogenic activities [1–3].Arsenic generally occurs as arsenic(V) and (III), depending on pH and redox conditions [1,4,5]. Arsenic(III) ismore toxic than arsenic(V), because arsenic(III) binds to single but with higher affinity to vicinal sulfhydrylgroups that reacts with a variety of proteins and inhibits their activity [6]. Arsenic(III) is more stable than As(V) because of electronic configuration. Long term ingestion of arsenic contaminated drinking water causesskin lungs and kidney cancer, gastrointestinal disease, bone marrow disorder, cardiovascular diseases andother diseases [7]. Due to extreme toxicity of arsenic in drinking water, World Health Organization (WHO,Geneva, Switzerland), Environmental Protection Agency (US-EPA, United States) [8,9] and Central PollutionControl Board (CPCB, India) [10,11] has set 0.01 mg L�1 and 0.05 mg L�1 as maximum permissible limit ofarsenic in drinking water. Many conventional processes for treatment of arsenic like adsorption [12,13],coagulation [12], co-precipitation [14], ion-exchange [15–18] and oxidation-reduction process have beenreported. Among all the process, the adsorption is one of the promising methods [12]. The aim of this workis to synthesize environment friendly hybrid material in lab scale and to study in detail for removalefficiency of arsenic(III) from water by using the material. The main objectives are: (a) synthesis andcharacterization of the hybrid material zirconium polyacrylamide, (b) to determine the kinetic parameter ofarsenic(III) adsorption, and (c) to study the effect of temperature, pH, time, initial concentration andcoexisting ions on the arsenic(III) adsorption. The present material which is synthesized in lab scale andsubsequently utilized for removal of arsenic(III) from water is not reported anywhere in the literature. Thisis a novel environment friendly hybrid material which can be utilized in small scale to large scale watertreatment for arsenic removal.

2. Materials and methods

2.1. Reagents and chemicals

All chemicals were used of analytical range (AR grade), which are obtained from E. Merck (Merck, India),Sigma-Aldrich (Sigma-Aldrich, United States), and Loba Chemie (Loba Chemie, India). Zirconium oxychloride (purityZ99.0%), ammonium persulfate (purity¼98%), bis-acrylamide (purity¼97%), hydroxy-methyl aminomethane (TRIS, purityZ99.8%), tetramethyl ethylenediamine (TEMED, purityZ99.5%), andarsenious oxide (purityZ99.9%), were used without further purification for the synthesis and experiments,borosil glassware was used to conduct all the experiments. All solutions are prepared in distilled water. 1 Lstock solution of arsenic(III) was prepared by dissolving 1.320 g arsenic trioxide (As2O3) in water containing4 g sodium hydroxide (NaOH) and diluted to 1 L; 1.00 ml¼1.00 mg arsenic(III), standard arsenic(III) solutionwere prepared for analysis by serial dilution of stock solution on daily basis.

2.2. Synthesis of zirconium polyacrylamide

Zirconium polyacrylamide was synthesized in the laboratory by the sol–gel method with water asa solvent by the following procedure. 52.8 ml of distilled water with 20 ml of 30% acrylamide mixture(acrylamideþbis-acrylamide) was taken, in a 250 ml round bottom flask, 15 ml of 1.5 M TRIS wasadded to maintain the pH 8.8 and 10 ml of 10% of zirconium oxychloride was added to the abovesolution with constant stirring. To this mixture, 1 ml of 10% ammonium persulphate and 0.2 ml ofTEMED as a catalyst and reaction initiator was added drop wise sequentially with vigorous stirring tomake a net volume of 100 ml. A white colored gel was formed, which was allowed for ageing at roomtemperature for 12 h. Then it was filtered and washed several times with distilled water to removeexcess reagent. The material is dried at 50 1C for 2 h in a hot air oven till it forms white granules.Finally the materials were kept in an air tight bottles until used. A series of same material wasprepared by varying the precursor's molar concentration and the best material having the lowest

Table 1Different composition of the hybrid material ZrPACM, surface area and particle size studies.

Material composition Molar ratio Particle size (nm) Surface area (m2/g)

ZrPACM-78 1:1 78.33 178.71ZrPACM-82 1:3 82.64 158.13ZrPACM-43 2:1 43.67 341ZrPACM-66 2:3 66.27 194.02ZrPACM-62 3:1 62.78 223ZrPACM-53 3:3 53.20 278.33

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particle size is obtained when the molar ratio is 2:1 (acrylamide mixture:ZrOCl2) and represented asZrPACM-43, which was taken for further optimization and removal studies (Table 1).

2.3. Characterization

The zirconium polyacrylamide was characterized by using various analytical instruments. Surfacemorphology of the material was examined using SEM (JEOL, JSM 6390LV, Japan) coupled with EDX(JEOL, JSM-6480LV) technique at an accelerating voltage of 20 kV. The surface charge density (s) ofsorbent was determined by a potentiometric titration method. The following equation was used todetermine the surface charge density:

so ¼ ððCA�CBþ½OH� ��½Hþ �ÞFÞ=m ð1Þwhere CA and CB were the molar concentrations of acid and base needed to reach a point on the titrationcurve, [Hþ] and [OH�] were the concentrations of Hþ and OH� , F was the Faraday constant(96,490 Cmol�1), m (g) was the mass of the sorbent. Surface area and pore volume were measuredusing a BET (Quantachrome Autosorb I, Boynton Beach, Florida) in N2 atmosphere by adsorption anddesorption technique. X-ray diffraction (XRD) data were obtained by a diffractometer by using PHILLIPSX'PERT X-ray diffractometer model PW 1830 (Almelo, Netherlands) with CuK radiation (35 kV and 30mA)at a scan rate of 31/min and was analyzed using standard software provided with the instrument. FTIRspectrometer spectrum RX I (Perkin-Elmer corporation, USA) are used to know various functional group ofthe adsorbent. FTIR were recorded at in 400–4000 cm�1 with a resolution of 4 cm�1 and 64 scans. Particlesize was analyzed by Malvern Nano ZS 90 (Malvern, UK). The thermogravimetric analysis was carried outwith a DTG-60 (DTG-60, Shimadzu corporation, Japan) in nitrogen atmosphere under a flow of30 ml min�1 and heating rate of 10 1Cmin�1 varying the temperature from 25 1C to 800 1C. The totalarsenic concentration was determined by using hydride generation technique and flame photometertechnique of AAS (Elico SL 176, India) using hollow cathode lamp (HCL) at wavelength range of 193.7–197.2 nm at slit width of 2.5 nm with EHT of 700 V and maximum current of 7.0 mA.

2.4. Adsorption Experiments

The extent of arsenic(III) removal was studied using batch mode of experiment which was carriedout by mixing adsorbent with fixed volume of arsenic(III) solution in 250 ml stopper glass bottle.Stoppers were used to avoid change in concentration due to evaporation. The mixture was agitated at400 r min�1 in a mechanical shaker (Remi Equipments, Mumbai, India) placed in an incubator, untilequilibrium was attained. After a predetermined contact time, the aqueous samples in each bottlewere decanted and centrifuged at 4500 r min�1 for 5 min and filtered through Whatman-42 filterpaper (pore size: 2.5 mm) and the arsenic concentration in the filtrate was measured using an atomicadsorption spectrophotometer (AAS). The experiments were conducted at variable dose (0.1–1.5 g/100 mL), pH (1–12), contact time (10–140 min), temperature (20–80 1C), and initial concentration(10–270 mg L�1). Where the optimum experimental conditions were ascertained, arsenic uptake bythe adsorbing material was calculated using the following equation:

Qe ¼ ðC0�CeÞV=W ð2Þ

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where Qe is equilibrium uptake (mg g�1), V is the volume of solution (L). C0 (mg L�1) is the initialconcentration of arsenic(III), Ce (mg L�1) is the concentration of arsenic(III) at equilibrium time “t” andW is the mass of the adsorbent material (g). In order to know the effect of other competing ions onarsenic(III) adsorption, studies were done by using anions (bicarbonate, carbonate, sulfate andnitrate). Solutions of these anions were prepared from their sodium and potassium salts. The initialconcentration of arsenic(III) was fixed at 10 mg L�1,while the initial concentration of other anionsvaried from 10 mg L�1to 270 mg L�1. The best fit models and error analysis of the present studieswere done by using Origin pro (version 8, origin lab corporation, USA) and MS-Excel (version 2010,Microsoft, USA) software. The best fit was disused using error bar plot, regression correlationcoefficient (R2), standard deviation (SD) and chi-square analysis (χ2).

3. Results and discussion

3.1. Characterization

The material is chemically stable as it is not soluble up to 3 M solution of mineral acids (H2SO4,HNO3 and HCl) and alkali (NaOH, NH4OH and KOH). The experiment was conducted in 30 ml ofdifferent mineral acids and alkali of different molar concentration for 24 h and supernatant liquid iscollected by filtration and analyzed for zirconium. The scanning electron microscopy withcorresponding EDS of material with and without arsenic loaded are presented in Fig. 1. The energydispersive spectrum (EDS) in the Fig. 1 shows the elemental composition of the material. There is a

Fig. 1. SEM and EDS of hybrid material ZrPACM-43: (a) before adsorption (b) after adsorption and (c) EDX micrographs ofbefore adsorption and after adsorption.

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remarkable change in the morphology and structure of the material when loaded with arsenic. It isclearly observed that crystals are embedded in the surface of the material after loaded with arsenic.The micrograph shows surface heterogeneity resulted from the adsorption of arsenic(III) on thesurface. The corresponding EDS spectrum indicates the presence of C, O, Zr and As. BET surface area ofthe material is found to be 341 m2 g�1. Powdered XRD diffractogramwas studied with PCPDFWIN andPhilips X'pert high score software to search for the phases of starting materials and adsorbedmaterials, powdered XRD diffractogram of the material before adsorption and after adsorption isrepresented in Fig. 2(a) and (b). Few sharp peaks are observed before and after indicating the sampleis crystalline in nature. The normal crystallite sizes of material were calculated using the DebyeScherrer equation [19]

Dð011Þð220Þ ¼ 0:9λ=ðβ2θ cos θmaxÞ ð3Þ

where D (plane of reflection at before adsorption (0 1 1) and after adsorption (2 2 0)) is the averagecrystal size in nm, λ is the specific wavelength of X-ray used, θ is the diffraction angle and β2θ is theangular width in radians at intensity equal to half of the maximum peak intensity. The crystallite sizewas found to be 53.60 nm and 238.00 nm before and after adsorption respectively, exact compositionwere drawn and compared by ICCD Database 1998 and represented in Fig. 2(a) and (b). The incrementin the crystallite size is may be due to increment in space charge polarization and crystal defects afteradsorption. FTIR studies were done in order to know the functional groups and structure of thepresent material. The spectrum of before adsorption and after adsorption is represented in Fig. 3(a) and (b). The presence of band at 3414.58 cm�1 is due to bonded OH groups, which indicates thepresence of water of crystallization. The NH2 stretching is overlapped with the band with a formationof spike; this peak is shifted to 3439.28 cm�1 after adsorption may be due to coordination of arsenic(III) with NH groups. The presence of next band at 2882.01 cm�1 in material is due to presence ofamide group which is shifted to 2994.19 cm�1 with slight broadening after adsorption. The peak at2818.95 cm�1 is due to combined stretching of N–H and O–H groups, the peak further shifted afteradsorption. The peak at 1612.42 cm�1 is due to C¼O stretching groups present in the structure, thepeak at 1200.00 cm�1 in the material is assigned to C–H and C–C stretching, the presence of peak atfinger print region 798.06 cm�1 and 618.35 cm�1 is due to C–N stretching and metal–oxygen bondingwhich is shifted to 745.88 cm�1, 618.73 cm�1 and 521.73 cm�1 after adsorption indicates theadsorption of arsenic. The TGA-DTA analysis of the material is presented in Fig. 4. The weight lossoccurred in the following three steps: (1) in the temperature range of 30–250 1C (21.37%) is due to lossof physical adsorbed water; (2) 53.74% in the temperature range of 250 1C to 580 1C is attributedmainly to the loss of lattice water and NH2 groups; and (3) 50.77% at higher temperature (580–700 1C)might be due to structural deformation, the DTA curve supported the above finding.

Fig. 2. X-ray diffraction pattern of hybrid material ZrPACM-43: (a) before adsorption and (b) after adsorption of arsenic(III).

Fig. 4. Thermogravimetric analysis and differential thermal analysis of hybrid material ZrPACM-43.

Fig. 3. FTIR spectrum of hybrid material ZrPACM-43: (a) before adsorption and (b) after adsorption of arsenic(III).

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The fresh adsorbent was analyzed to obtain its elemental composition by CHNS Elementar andEDS. The results indicate the elemental composition as Zr 16.82%, O 28.08%, C 14.80%, H 3.11%, and N2.88%, and others 34.31%. Based on the above studies of FTIR, TGA-DTA and the elemental analysis, themolecular formula of the adsorbent was deduced by using the Alberti equation [20].

18n¼ XðMþ18nÞ=100 ð4Þ

where X is the percent of water content and (Mþ18) is the molecular weight of the material. It givesthe value of “n” as 2.40, the tentative empirical formula for the material can be suggested as [(ZrO2)(C4H7NO)] �nH2O. The zero point surface charge density of the hybrid material as a function of pHis studied and represented in Fig. 5. The study shows that the surface holds positive charge in lower

Fig. 5. Surface charge density as a function of pH (m¼1 g L�1) for hybrid material ZrPACM-43.

Fig. 6. Variation of adsorbent dose on the percentage removal of arsenic(III) by the hybrid material. Experimental conditions:pHr5, temperature: 26 1C, contact time: 60 min, and stirring speed: 20 r min�1.

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pH value, the surface charge density decreases when the solution pH increases. The pH of zero pointsurface charge density was recorded around 4.8 (pHzpc). The value of pHzpc is positive as solution pH isless than 5, however the surface acquires negative charge as the solution pH is higher than 5.

3.2. Effect of adsorbent dose, pH, and initial arsenic concentration on the removal of arsenic (III)

The effect of adsorbent dose on removal of arsenic(III) was studied at pHr5, stirring speed of20 r min�1 at temperature 26 1C and represented in Fig. 6. As expected the removal of arsenic(III)increases from “47% to 98.22%, 43.25% to 96.87% and 41.79% to 93.56%” with increase in adsorbentdose from 0.1 to 1.5 g/100 ml respectively at a selected contact time of 60 min keeping initial soluteconcentration at 10 mg L�1, 50 mg L�1 and 100 mg L�1. It is found that after dosage of 13 g L�1, thereis no significant change in percentage removal of arsenic. The increase in percentage removal could be

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attributed to the availability of more number of adsorption sites at the solid phase. Availability ofspecific surface area and micropore volume plays a vital role for surface adsorption process. However,in present investigation, with further increase in adsorbent dose, the removal extent remains almostconstant indicating the saturation of adsorption sites. The saturation of the active sites may also bedue to the overlapping of active sites at higher dosage as well as the decrease in the effective surfacearea resulting in the accumulation of exchanger particles. So, 13 g L�1 is considered as the optimumdose and is used for further study.

Percentage removal of arsenic at different pH (1–12) was studied using 13 g L�1 of adsorbent doseat room temperature (26 1C), and contact time of 60 min for initial arsenic(III) concentration of10 mg L�1, 50 mg L�1, and 100 mg L�1. The results are presented in Fig. 7. There is no change in thesolution pH after addition of adsorbent and solution remains at pH 7. It is evident from the graph thatthe highest removal is “97.06% for 10 mg L�1, 94.84% for 50 mg L�1 and 87.62% for 100 mg L�1

respectively” at pHr5. The removal of arsenic decreases with increase in pH may be due to thefollowings. (1) When the concentration of Hþ ions is more in water solution, then the magnitude ofpositive charge over amino group is more and (2) competition for active sites by excessive amount ofhydroxyl ions present in the water in alkaline pH [21], the above attained pH indicates a goodagreement with zero point surface charge (pHzpc) study.

3.3. Contact time and adsorption kinetic studies

The effect of contact time on the removal of arsenic(III) was studied in the range of 10 min to140 min by using 13 g L�1 of adsorbent at room temperature (26 1C), at pHr5. From the Fig. 8, it isunderstood that the effective removal achieved within 120 min, which is “98.67%, 96.32% and 92.67%”for initial concentration of 10 mg L�1, 50 mg L�1 and 100 mg L�1 respectively. After 120 min there isno change in removal percentage, so 120 min was considered as the effective equilibrium time foradsorption. Initially the rate of removal is higher, which may be due to more vacant sites foradsorption in the adsorbent and having high solute concentration gradient.

In order to examine the controlling mechanisms of adsorption process such as mass transfer andchemical reaction, several kinetic models like Lagergren first order rate equation and second orderrate equation are used to test the experimental data using initial concentration of 10 mg L�1,50 mg L�1 and 100 mg L�1. The integrated linear pseudo-first order rate equation and second order

Fig. 7. Effect of pH on the removal of arsenic(III) by hybrid material ZrPACM-43. Experimental conditions: dose: 13 g L�1,temperature: 26 1C, contact time: 60 min, and stirring speed: 20 r min�1.

Fig. 8. Effect of contact time on the removal of arsenic(III) by hybrid material ZrPACM-43. Experimental conditions: dose:13 g L�1, temperature: 26 1C, pHr5, and stirring speed: 20 r min�1.

Table 2Rate constants (K1), and (K2), were obtained from the graph for removal of arsenic(III) by hybrid material at different initialconcentrations.

Pseudo first order Second order

K1 R2 SD K2 qc R2 SD

ZrPACM-43hybrid material

10 mg L�1 0.04 0.99 0.03 1.57 1.57 1.00 0.0150 mg L�1 0.04 0.92 0.08 0.12 7.79 1.00 0.03100 mg L�1 0.05 0.92 0.11 0.07 15.37 1.00 0.15

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rate equation are represented as [22,23]

Logðqe�qtÞ ¼ Log qe�K1ft=2:303g ð5Þ

t=qt ¼ ½1=ðK2q2c Þþ1=qc�t ð6Þ

where qe and qt (both in mg g�1) are the amount of arsenic(III) adsorbed at equilibrium and at time “t”respectively, K1 is adsorption rate constant of pseudo-first order adsorption, K2 is the rate constant ofsecond order rate equation (g mg�1 min�1), and qc is the maximum adsorption capacity (mg g�1) forthe second order adsorption. The values obtained from the plots were represented in Table 2.

3.3.1. The best fit modelThe evaluation of the best active kinetic models for fitting the adsorption data was made by

standard deviation (SD) and correlation coefficient (R). The SD values and correlation coefficient ofmaterial for all kinetic models are shown in Table 2. Lower SD values and good correlation coefficientwere observed for second order kinetic model, which indicates the best fit model and significant indescribing the arsenic(III) adsorption process.

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3.4. Effect of temperature

The effect of temperature upon adsorption process was studied with variation of temperature from20 1C to 80 1C. Various thermodynamic parameters such as ΔGT, ΔST and ΔHT were also calculated. Theexperimental observation indicated that within the range of study, the percentage of uptake of arsenic(III) by the adsorbent material increases from “67.28% to 97.33%, 60.02% to 94.87% and 55.40% to90.57%” for initial concentration of 10 mg L�1, 50 mg L�1 and 100 mg L�1 respectively. The highestremoval efficiency was at 50 1C for all the initial concentration, which is considered as optimumtemperature. The thermodynamic feasibility of adsorbent–arsenic interaction process can berepresented as [24,25]

ΔG0 ¼ �RT ln Kc ð7Þ

Kc ¼ Ca=Ci ð8Þ

Log Kc ¼ ½ðΔSTÞ=R�ðΔHTÞ=RT � ð9Þ

ΔGT ¼ΔHT�TΔST ð10Þwhere Ca and Ci are the amount of arsenic(III) ion adsorbed per unit mass of adsorbent andconcentration of arsenic(III) ion in aqueous phase, Kc is the equilibrium constant, R is the universal gasconstant (8.314 J mol K�1), T is the temperature (K), ΔGT, ΔST and ΔHT are the changes in Gibb's freeenergy, entropy and enthalpy of adsorption respectively. The value of ΔHT and ΔST were evaluatedfrom the slope and intercept of the plot log Kc versus 1/T. The results of analysis are represented inTable 3. The negative values of ΔGT at all temperature confirm the spontaneous nature of adsorption.The positive values of ΔHT confirm the feasibility of the reaction and indicate the endothermic natureof adsorption. The decreasing value of ΔGT with temperature shows the reaction is more feasible athigher temperature.

3.5. Adsorption isotherm

The relationship between the equilibrium of arsenic(III) adsorbed and the solute concentration wasverified using various isotherms. In the present work three isotherm models i.e. Langmuir, Freundlich,and Dubinin–Radushkevic (D–R) were used to find the best fitted model. The studies were done atdose of 13 g L�1, temperature of 50 1C, time of 120 min and at pHr5. The linearized form of theLangmuir, Freundlich and D–R is given below [26–28].

Langmuir model (linear)

1=qe ¼ 1=ðq0bCeÞþ1=q0 ð11Þwhere, qe is the amount of arsenic(III) adsorbed at equilibrium (mg g�1), Ce is the equilibriumadsorbate concentration (mg L�1), the values of Langmuir constants b (binding energy constant) andqo (mono layer adsorption capacity in mg g�1) relates to the energy and capacity of adsorption process.The isotherm criterion can be described by another dimensionless constant, which is otherwise known

Table 3Thermodynamic parameters for arsenic(III) removal by hybrid material.

ΔHT

(kJ mol�1)ΔST

(kJ K�1 mol�1)ΔGT

10 1C 15 1C 20 1C 25 1C 30 1C 35 1C 40 1C

ZrPACM-43hybridmaterial

10 mg L�1 140 0.383 �136.2 �134.3 �132.3 �130.4 �128.5 �126.6 �124.750 mg L�1 144 0.257 �141.7 �140.4 �139.1 �137.8 �136.5 �135.2 �133.9100 mg L�1 149 0.364 �145.4 �143.5 �141.7 �139.9 �138.1 �136.2 �134.4

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as separation factor or equilibrium parameter r as represented in the following equation:

r¼ 1=ð1þbC0Þ ð12Þwhere C0 is the initial concentration of arsenic(III) (mg L�1) and r is the Langmuir isotherm constant.The feasibility of isotherm can be evaluated from the values of r, where ro1 represents favorableadsorption and r41 represents unfavorable adsorption processes. The calculated value of r for the initialarsenic(III) concentration of 10 mg L�1, 50 mg L�1 and 100mg L�1 was found to be 0.07, 0.014 and 0.007respectively. The adsorption capacity was found to be 41.48 mg g�1 obtained from the linear plot of 1/qeversus 1/Ce.

Freundlich model (linear)

Log qe ¼ Log K f þ1=ðn log CeÞ ð13Þwhere Freundlich constants Kf and 1/n are the adsorption capacity and adsorption intensityrespectively represented in Table 4. The values were obtained from the linear plot of log qe versuslog Ce and represented in Fig. 9. Higher the value of 1/n, the higher will be the affinity between theadsorbate–adsorbent and the heterogeneity of the adsorbent sites. In present investigation, thecalculated value of 1/n was found to be 0.804 indicating that it is valid for the active adsorption sitesand contain equal energy for adsorption process as studied by using the D–R model (linear)

ln qe ¼ ln qm�K2ε ð14Þ

ε¼ RT lnð1þ1=CeÞ ð15Þ

E¼ �ð2KÞð�1=2Þ ð16Þwhere ε is Polanyi potential, qm is the hypothetical adsorption capacity, K is the constant related toadsorption energy, R is the universal gas constant (8.314 J mol�1 K�1) and T is the temperature in Kelvin,represented in Fig. 10. The value of K and qm, respectively, is obtained from the slope and intercept of the

Table 4Various isotherm parameters for removal of arsenic(III) by hybrid material.

Isotherm models ZrPACM-43 hybrid material

Parameters Values

Langmuir isotherm constants qo (mg g�1) 41.49b (L mg�1) 1.40R2

0.9510.941

χ2 5.28

Langmuir dimensionless equilibrium parameter (r) 10 mg L�1 0.0750 mg L�1 0.014100 mg L�1 0.007

Freundlich isotherm constants Kf (mg g�1) 0.20N 1.24R2

0.9890.993

χ2 1.16

D–R isotherms K (mol2 kJ�2) 8.07�10�7

qm (mg g�1) 0.80E (kJ mol�1) 787.01R2

0.9030.997

χ2 0.42

Fig. 9. Freundlich adsorption isotherm study for the arsenic(III) removal by hybrid material ZrPACM-43. Experimentalconditions: dose – 13 g L�1, temperature – 50 1C, contact time – 120 min, stirring speed – 20 r min�1, and pHr5.

Fig. 10. D–R adsorption isotherm, for arsenic(III) removal by hybrid material ZrPACM-43, Experimental conditions: dose –

13 g L�1, temperature – 50 1C, contact time – 120 min, stirring speed – 20 r min�1, and pHr5.

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plot qe versus ε2. The value of Kwas found to be 8.07�10�7 mol2 kJ�2 and that of qm was 0.8026mg g�1,the mean free energy of adsorption (E) was calculated from the constant K using the relation.

The value of E is very useful in establishing the type of adsorption. The values originate in thepresent experiment was 787.011 kJ mol�1 which is higher than 400 kJ mol�1, and which indicates thepresent process is chemisorption.

3.5.1. The best fit modelThe best fit model for the isotherm studies were calculated by correlation coefficient and

Chi-square analysis. However the data are calculated by using the software. The results of correlationcoefficient and Chi-square analysis were represented in Table 4. The lower χ2 and good correlationcoefficient values of Freundlich and D–R suggest the applicability of the best fitting model for theadsorption of arsenic on ZrPACM-43 hybrid material, then Langmuir.

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3.6. Mechanism of adsorption of arsenic(III) on ZrPACM-43 hybrid material

A mechanism for the adsorption of arsenic(III) by hybrid material has been proposed by taking theresults obtained from the experimental findings and computing the results using mathematical/theoretical models. The mechanism of arsenic removal by the hybrid material was governed byelectrostatic adsorption and complexation for which a mechanism is proposed as represented inFig. 11. At acidic pH, the material gets positively charged due to the protonation of amino groupswhich remove hydrogen arsenite ion by means of acidic solution which demonstrates a positive redoxpotential (þ0.6 V), On the variation of pH, these surface active OH groups may further bind or releaseHþ where the surface remains positive due to the following reaction:

MOHþH3Oþ-MOH2þH2O ð17Þ

The above reaction indicates that the removal efficiency of the material is more at low pH. Thus, whenpHr5.00, the overall arsenite adsorption mechanism can be represented in two different forms:

(a)

Electrostatic interaction between positively charged center (nitrogen) and negatively chargedarsenite molecule in solution (Eq. (18)).

(b)

Electrostatic attraction and complexation between positively charged surface hydroxyl group andarsenite (Eq. (19)).

MNH2þþHAsO3

3�-MNH2þ–HAsO3

3� (18)

MOHþH3OþþHAsO33�-MOH2

þ–HAsO33�þH2O (19)

Fig. 11. Proposed mechanism for arsenic(III) removal by hybrid material ZrPACM-43.

S. Mandal et al. / Water Resources and Industry 4 (2013) 51–6764

This information was supported by the formation of arsenic(III) complexes which is colorless. Thepresence of arsenic peak in the EDS and XRD spectra of arsenic sorbed hybrid material confirms theoccurrence of arsenic sorption onto the hybrid materials.

The modeling of the specific adsorption of arsenic(III) on any material surface depends on anumber of external factors such as temperature, pH, initial concentration, as well as the density ofsurface functional groups available for coordination. In light of the above-mentioned mechanism ofadsorption, it may be further noted that the material showed adsorption capacity at a wide acidic pHrange, which could be useful for commercial exploitation purpose; a comparative study is representedin Table 5 for removal of arsenic(III) by different hybrid materials and composites reported in theliterature.

3.7. Effect of competitive ions and regeneration of adsorbent

The effect of various diverse ions/competing co-ions upon adsorption of arsenic were investigatedusing chloride, bicarbonate, nitrate, sulfate. The experimental condition for initial arsenic(III)concentration was kept at 10 mg L�1 varying the initial concentration of anions from 10 mg L�1 to270 mg L�1. It was observed that presence of all these anions reduces the adsorption process. Thereduction on adsorption follows the following order by anions sulfate4chloride4carbonate4bi-carbonate4nitrate. These ions may be competing for the active sorption sites along with the arsenicduring adsorption process which resulted in decrease in adsorption capacity. Apart from this, theeffect of these anions towards adsorption may be due to their affinity towards the adsorbent material.Regeneration studies were carried out in order to know the reusability of the hybrid material. Theregeneration percentages and reusability of the hybrid material are represented in Fig. 12(a) and (b).Percentage regeneration of the adsorbed arsenic(III) in aqueous solution resulted about 99.78%,94.51% and 90.12% at pH 10 for initial concentration of 10 mg L�1, 50 mg L�1 and 100 mg L�1

respectively, which indicate that the material can be easily regenerated by alkali and used for severalcycles. The reusability studies of the material were done and it was found that the material can bereused up to eight cycles (60% removal).

4. Conclusion

In this study a new zirconium polyacrylamide a novel hybrid material is used for the removal ofarsenic(III) from synthetic water. The SEM, EDS, XRD and FTIR analysis confirms the arsenicadsorption; the TGA-DTA reveals that the material is stable up to 680 1C. The lowest particle size

Table 5Various hybrid materials/composites and there arsenic removal capacities obtained.

Sl.no.

Different hybrid materials Adsorptioncapacity/density

Ionsremoved

Methodsused

Isotherm supported References

1 Fe(III)/La(III)-chitosan 109 mg g�1 As(III) andAs(V)

adsorption – [29]

2 Hybrid (polymeric/inorganic),fibrous sorbent, (FIBAN-As)

75.67 mg g�1

81.66 mg g�1As(III) andAs(V)

adsorption Langmuir [30]

3 Fe(II) loaded and Fe(III) loadedapricot, stone-based ACs

2.023 mg g�1,3.009 mg g�1

As(III) andAs(V)

adsorption Freundlich andDubinin–Radushkevich

[31]

4 Al-HDTMA-sericite, (AH) 0.433 mg g�1,0.852 mg g�1

As(III) andAs(V)

adsorption Langmuir andFreundlich

[32]

5 Hydrous iron(III) oxidepolyacrylamide

43.0 mg g�1 As(V) adsorption – [33]

6 GFH (granular ferric hydroxide) 8 mg g�1 As(III) adsorption Freundlich [34]7 Laterite soil 69.22 mg L�1 Total

arsenicadsorption Langmuir, D–R [35]

8 ZrPACM-43 (present material) 0.20 mg g�1,0.80 mg g�1

As(III) adsorption Freundlich, D–R Presentmaterial

Fig. 12. Regeneration and reusability of the hybrid material ZrPACM-43: (a) regeneration percentage and (b) reusability of thehybrid material (experimental conditions: dose – 13 g L�1, time: 120 min, temperature: 50 1C and strring speed: 20 r min-1).

S. Mandal et al. / Water Resources and Industry 4 (2013) 51–67 65

obtained for the hybrid material synthesized was 43 nm with maximum surface area of 341 m2 g�1.The maximum removal efficiency of arsenic(III) was 98.22% under optimum conditions of adsorbentdose 13 g L�1, pH of the solutionr5, contact time of 120 min and temperature 50 1C. The adsorptionprocess followed second order kinetics with correlation coefficient of 0.999. The adsorption data arebest supported to Freundlich model and D–R model with maximum adsorption capacity of 0.20 and0.80 mg g�1. The langmuir adsorption capacity was found to be 41.48 mg g�1. The study of anioneffect in the adsorption process shows that the adsorption decreases in order of anions;sulfate4chloride4carbonate4bicarbonate4nitrate. The regeneration study indicates that thematerial can be easily regenerated by using alkali at maximum pH of 10. The reusability studysignifies that the material can be easily reused up to eight cycles with maximum removal of 60%. Fromthe above study it is clearly concluded that the material can be suitably used for removal of arsenic.

S. Mandal et al. / Water Resources and Industry 4 (2013) 51–6766

Conflict of Interest

The authors declare no conflict of interest.

Acknowledgments

S Mandal is thankful to University Grant Commission, (UGC-RGNF) [F.14-2(SC)/2010(SA-III)] forproviding the financial supports. The authors are also thankful to Prof. Sunil Kumar Sarangi, Director,and Prof. B.G. Mishra, HOD, Chemistry, NIT Rourkela for all other supports.

References

[1] D. Mohan, P. Charles, Arsenic removal from water/wastewater using adsorbents– a critical review, Journal of HazardousMaterials 142 (1–2) (2007) 1–53.

[2] Y.S.T. Choong, G.T. Chuah, H.Y Robia, L.F.G. Koay, I. Azni, Arsenic toxicity, health hazards and removal techniques fromwater:an overview, Desalination 217 (2007) 139–166.

[3] S. Shevade, R. Ford, Use of synthetic zeolites for arsenate removal from pollutant water, Water Research 38 (2004) 3197–3204.[4] L. Lorenzen, J.S.J. Van Deventer, M.W. Landi, Factors affecting the mechanism of the adsorption of arsenic species on

activated carbon, Minerals Engineering 8 (4) (1995) 557–569.[5] F. Di. Natale, A. Erto, A. Lancia, D. Musmarra, Experimental and modelling analysis of As(V) ions adsorption on granular

activated carbon, Water Research 42 (2008) 2007–2016.[6] H.V. Aposhian, R.M. Maiorino, R.C. Dart, D.F Perry, Urinary excretion of meso-2, 3-dimercaptosuccinic acid in human

subjects, Clinical Pharmacology & Therapeutics 45 (5) (1989) 520–526.[7] IARC, Overall evaluation of carcinogenicity to humans. As evaluated in IARC monographs vol. 1–73, 1998, ⟨http://www.iarc.

htm⟩ (updated November 30, 1998).[8] WHO, Exposure to arsenic: a major public health concern, WHO Document Production Services, Geneva, Switzerland, 2010.[9] EPA, Environmental Protection Agency, Environmental Pollution Control Alternatives, EPA/625/5-90/025, EPA/625/4-89/

023, Cincinnati, US, 1990.[10] M.J. Maushkar, Guidelines for water quality monitoring, Central pollution control board (A Government of India

organisation), Delhi, India, 2007.[11] BIS, (Bureau of Indian Standards) 10500, Indian Standard Drinking Water Specification; First revision, vol. 1–8, Bureau of

Indian Standard Publication, New Delhi, India, 1991.[12] S.W. Wan Ngah, C.L. Teong, M.K.A.M. Hanafiah, Adsorption of dyes and heavy metal ions by chitosan composites a review,

Carbohydrate Polymers 83 (2011) 1446–1456.[13] A. Afkhami, M. Saber-Tehrani, H. Bagheri, Simultaneous removal of heavy-metal ions in wastewater samples using nano-

alumina modified with 2,4-dinitrophenylhydrazine, Journal of Hazardous Materials 181 (2010) 836–844.[14] Z. Wu, M. He, X. Guo, R. Zhou, Removal of antimony(III) and antimony(V) from drinking water by ferric chloride

coagulation: competing ion effect and the mechanism analysis, Separation and Purification Technology 76 (2010) 184–190.[15] R.K. Misra, S.K. Jain, P.K. Khatri, Iminodiacetic acid functionalized cation exchange resin for adsorptive removal of Cr(VI), Cd

(II), Ni(II) and Pb(II) from their aqueous solutions, Journal of Hazardous Materials 185 (2011) 1508–1512.[16] F. Fernane, M.O. Mecherri, P. Sharrock, M. Hadioui, H. Lounici, M. Fedoroff, Sorption of cadmium and copper ions on natural

and synthetic hydroxylapatite particles, Materials Characterization 59 (2008) 554–559.[17] A. Dabrowski, Z. Hubicki, P. Podkościelny, E. Robens, Selective removal of the heavy metal ions from waters and industrial

wastewaters by ion-exchange method, Chemosphere 56 (2004) 91–106.[18] S.K. Nataraj, K.M. Hosamani, T.M. Aminabhavi, Nanofiltration and reverse osmosis thin film composite membrane module

for the removal of dye and salts from the simulated mixtures, Desalination 249 (2009) 12–17.[19] N.H Tran, A.J. Hartmann, R.N. Lamb, Structural order of nanocrystalline ZnO films, Journal of Physical Chemistry B 21 (1999)

4264–4268.[20] G. Alberti, E. Torracca, A. Conte, Journal of Inorganic and Nuclear Chemistry 28 (1966) 607.[21] F. Amiri, M.M. Rahman, H. Bornick, E. Worch, Sorption behaviour of phenols on natural sandy aquifer material during flow-

through column experiments: the effect of pH, Acta Hydrochimica et Hydrobiologica 32 (3) (2004) 214–224.[22] S. Lagergren, To the theory of so-called adsorption of dissolved substances, The Royal Swedish Academy of Sciences 24

(1889) 1–39.[23] J. Wang, L. Zhao, Han L. Duan, Y. Chen, Adsorption of aqueous Cr(VI) by novel fibrous adsorbent W with amino and

quaternary ammonium groups, Industrial and Engineering Chemistry Research 51 (2012) 13655–13662.[24] P.V. Messina, P.C. Schulz, Adsorption of reactive dyes on titania–silica mesoprous materials, Journal of Colloid and Interface

Science 299 (2006) 305–320.[25] C. Namasivayam, R.T. Yamuna, Adsorption of direct red 12 B by biogas residual slurry: equilibrium and rate processes,

Environmental Pollution 89 (1995) 1–7.[26] Langmuir, The adsorption of gases on plane surfaces of glass, mica, and platinum, Journal of the American Chemical

Society 40 (9) (1918) 1361–1403.[27] H. Freundlich, About the adsorption in solutions, Zeitschrift für Physikalische Chemie 57 (1906) 384–470.[28] C. Raji, T.S. Anirudhan, Batch Cr (VI) removal by polyacrylamide grafted sawdust: kinetics and thermodynamics, Water

Research 32 (12) (1998) 3772–3780.

S. Mandal et al. / Water Resources and Industry 4 (2013) 51–67 67

[29] R.N. Shinde, A.K. Pandey, R. Acharya, R. Guin, S.K. Das, N.S. Rajurkar, P.K. Pujari, Chitosan-transition metal ions complexesfor selective arsenic(V) preconcentration, Water Research 47 (2013) 3497–3506.

[30] O.M. Vatutsina, V.S. Soldatov, V.I. Sokolova, J. Johann, M. Bissen, A. Weissenbacher, A new hybrid (polymer/inorganic)fibrous sorbent for arsenic removal from drinking water, Reactive and Functional Polymers 67 (2007) 184–2001.

[31] Tuna Hunter (Avc) Ozge Asli, Ozdemir Ercan, Lightning(Şimşek) Bilgin Esra, Cup (Beker) Ulker, Removal of As(V) fromaqueous solution by activated carbon-based hybrid adsorbents: impact of experimental conditions, Chemical EngineeringJournal, 223, 116–128.

[32] D. Tiwari, S.M. Lee, Novel hybrid materials in the remediation of ground waters contaminated with As(III) and As(V),Chemical Engineering Journal 204–206 (2012) 23–31.

[33] Y. Shigetomi, Y. Hori, T. Kojima, The removal of arsenate in waste water with an adsorbent prepared by binding hydrousiron(III) oxide with polyacrylamide, Bulletin of the Chemical Society of Japan 53 (1980) 1475–1476.

[34] M. Badruzzaman, P. Westerhoff, D.R.U. Knappe, Intraparticle diffusion and adsorption of arsenate onto granular ferrichydroxide (GFH), Water Research 38 (18) (2004) 4002–4012.

[35] S.K. Maji, A. Pal, T. Pal, Arsenic removal from real-life groundwater by adsorption on laterite soil, Journal of HazadousMaterials 151 (2–3) (2008) 811–820.